Apparatus for stretching sheet material



July 18, 1950 J. MAHLER 2,515,830

APPARATUS FOR STRETCHING SHEET MATERIAL Filed Oct. 19, 1946 2 Sheets-Sheet 1 July' 18,1950 J, MAHLER 2,515,830`

APPARATUS FOR STRETCHING. SHEET MATERIAL Filed oct. 19. 194e v 2 sheets-sheet z Patented July 18, 1950 f ArPAnA'r'Us FOR.' STRETCHING SHEET MATERIAL Joseph Mahler, Brookline, Mass., assigner to American Optical.

Company,

Southbridge,

Mass., a voluntary association of Massachusetts Application October 19, 1946; Serial No. 704,413

This invention relates4 to apparatus for making light polarizers` and more` especially to a curvilinear `polarizer capableA of lamination to a curved surface, such as an optical lens.

It nowwellv knownlthat the moleculesi'of certain groups of plastics, suchV as cellophane and polyvinyl alcohol; can be oriented into par-` allelism and, when such plastics so treated are stain'edwith a polarizing dye, for example, a`

dichroic dye,` a light polarizeris formed. The

plastics aforesaid cannot be stretched to elfectL the orientation. of the molecules thereof untill they have been softened by' heating. When a sheet of plastic is softenedV by heating and then stretched tosecure the desired orientation yof its molecules', the'v plastic is likely to split in the direction in ywlciichhit. is stretched, which, of

course, is the direction Vof the orientation, of its' For thisreasonit is impossible to' molecules. laminate such- `'materialto curved surfaces; in fact, the lamination?thereof to flat surfaces isv dilcult and is successful only when great care is used.

In order to handle a `iilmA which has beenl stretched after heating, it is necessary to secure it` to a film base, such ias celluloseacetate or the like. A polarized film anchored tov a base` lilm cannot be laminated to a curvedl lens or between two `curved lenses because the base,` being stift, does notrea'dily assume the curvature ofthe lens or lenseslor adhere thereto.

Another diiiiculty preventing the lamination of a polarizer having itsmolecules oriented in linear parallelism toca curved lens or between' curved lenses is that-1` a substantial distortion of the polarizer will result when it is forced out.. of its original plane surface to assume the con figuration of the lens.- Y -v w y When a sheet of suchplastics hasbeen sof'- tened by heat and'stretched to orient the molecules thereof, thefsurface' of the nlm is hardened to such an extent that a dichroic dye. cannot readily penetrate the surface thereof and if the time of treatment is extended in order to secure the necessary penetra-tion, the distribution of. the dye lis not uniform even in small areas.

Ity is highly desirable that` a polarized slm..

glass, if used by one whose vision` is defective,

should comprise optical glass lenses ground accordance with the lenses of the spectacles worn` by such user. Ii the user' does not have' defective vision requiring correction by spectacles, it is desirable-that thepolarized nlm of his sun glasses should be laminated to a lcurvilinear` surface for the" reason that when the polari-zer 4 Claims. i (Cl. 18-,-19)

I is laminated' to a plane impinging upon the rearward surface of the glasses.

i IIt is-therefore one of the objectsv of'myinfvention to provide an apparatus, for makinga curvilinear polarizer having such qualities` that it is capable of lamination to a curvilinear surf,

facewithoutsplitting. Another object is to: provide an material having its molecules oriented` curvilinearly, that is to say, one having its molecules oriented on both sides of its longitudinal axis,

theorientation on each of the sides of the sheetk being coni/exto that of the other.

Another object isto provide a simple land eiective device for stretching a sheet o i plasticu to orient the molecules thereof.

Other objects of my invention will appear from the `detailed description of the particular yemu bodiments thereof. selected to explain the principles underlying the same.

In the drawings: Figure 1 is a plan view of one the molecules thereof. f

Fig. 2 is a sideview of the same.

Fig. 3 is a side view partlyin section of upper side of said device.

Fig; 4v is a section taken on Fig. 1.

Fig.'5 is an elevation of one form of gauge, that` may be used with the stretching device. Fig.6 isa plan view cn a smaller scale indieating a curvi-linearly polarized nlm. and the-A curvilinear lens to which it is to be laminated.

Fig. '7 is a plan view of two curvilinear` lenses;

having a polarized iilm laminated thereto.

Fig..8 is a section on the line B---of Fig. Figs. 9, 10, 11, and `12, are diagramsillustratf,

ing the several stages in the4 lamination oimy polarizer between two curvilinear lenses.

I have found that when a sheet of polyvinyl. alcohol or cellophane, each of which `is water. soluble, is treated with a suitable reagent inthe-` manner hereinafter set forth, the physical char,I

acteristics of such sheet are so altered that the sheet is of low water solubility, in fact, practically water insoluble, has high flexibility whenin` moistened condition, is readily stretchable at y. room temperatures, (20 C.), `or even at as low as 1 C.,. to orient its molecules and is caf-f pable oi application to a curved surface, assume..

ing: the shape thereof without splitting; in the surface, the glasses forni a mirror which reects intothe usersv eyes, light.-

ap;paratus for making a lamination or sheet of polarized.

form of device1 that may be used for stretching a film to orient,

the line 1 -4. off

direction of orientation and that said sheet, if stained with a dichroic or other suitable dye, becomes an eflicient polarizer.

It is to be understood, however, that I do not limit myself to the plastics above named.

I have found that suitable reagents fortreating n a sheet of polyvinyl alcohol are solutions of allkalii;- metal salts, such, for example,`as 'a solution of' sodium sulphate having a concentration of about, ,v r1() (monobasi'c) or potassium/ 100 grams per liter of water or a solution of sodium phosphate phosphate (monobasic) of about the same con;A

centration. While sodium sulphate (monobasic),

sodium phosphate (monobasic)l and sodium sulphate work particularly well, it is to be understoodA that my invention is not limited specically to the used with good results.

,A use of these reagents, for resorcinol may'also be The time of treatment of the sheet depends Y i upon its thickness and the temperature of the bath, for example, for a sheet of plastic havingl av thickness of about .003 inch, and a bath temperature of about 1 C., the time of treatment will be about three minutes and if the temperature of the bath is about 20 C., such time will beaboutone minute. l

If the plastic to be treated is cellophane, I pref` fer a caustic alkaline hydroxide, such, for exam-i ple, as sodium hydroxide or potassiumhydroxide, and such sheet so treated will have substantially the same characteristics as those above set vforth with respect to polyvinyl alcohol.

A sheet of either of the materials treated asl above will readily accept a dichroic or other suit;l able dye which will almost instantaneously*dis"-4 tribute itself uniformly into the plastic after the molecules thereof have been oriented, thereby making a polarizer of the proper density and shade.

While at the present time I prefer sodium sulphate as a reagent for giving polyvnyl'alcoholf the .propertiestoutlined above, it is to' be 'und'erfz stood that sodium sulphate and potassium'phos-l 'f phate (monobasic) are full chemical equivalents, producing products which aside from their differences in degree of water solubility andacidity arey iull chemical equivalents and that sodium-phosphate is the chemical equivalent` of phosphate, for this purpose; y

When the molecules of the substances above described are orientedcurvilinearly, there will be two sets of such oriented molecules, one on either potassium side of the axis of'stretch of the film; that is'toV say, the central longitudinal axis, if, as shown in Fig. 1, the film is stretched longitudinally, as indicated by the arrow, and the orientation on'on'e" of the sides of the film will be convex to that of' the other. l

I consider as embraced within the vscope of my invention all other vplastics which when ltreated with suitablereagents will be of low-water solubility, high iiexibility when in `moistened condi? tion, stretchable at a temperature as low as 1f CJ, or lower, for curvilinearly orienting their mole,n

cules in the manner above stated, and capableof lamination to a curvilinear surface and assumingv the shape thereof without splitting in thedirecl tion of orientation.

There is shown in Fig. 1, a stretcher which vI have found convenient for orienting the molecules of plastic sheets treated as above set forth.l The stretcher comprises two attened U -shaped members I hinged together in any suitable manner,A In the present instance, thet as indicated at II. attened lower ends of the side members I2 take brace and snap over the latter to securely hold the ends of the sheet to be treated to the cross bars. Each said clip has a circumferential length slight- 1y greater than 180, and the outer edges thereof are iiar'ed outwardly, as shown at I6. The free edge of each clip terminates in a nger piece I6 extending beyondthe cross bars.

,Any suitable holder may be employed to retain th'e's'tretcher in semi-closed position, preparatory to clamping the ends of 'a sheet of plastic to the cross bars. In Fig.v 5, I have shown such holder comprising the plates II, which are pivoted to a bracket rising from the base I8. v The angle be' tween the `plates which, of course, governs the angle between the side'members of the stretcher having been determined, the plates may be' clamped to the semi-circular guide I9 by screws 20.

them, as indicated in Fig. 5. The ends of the lm are now placed over the bars I5 and irmly` clamped thereto by the clips I6, one of which, in'

Fig. 5, is shown in open position. By way of example, the length of the film 23 before stretching may be one inch. The stretcher will now be re-V moved from the holder and immersed in the chemical bath above specified, and after remaining there the proper length of time, the side memy bers of-the stretcher will be rotated about theirv thev pivot until the two U-shaped members lie in same plane.

The degree of stretch, that is, the ratio of the" length of the plastic sheet after stretching to its original length is subject to the widest latitude I have found that a suitable curvilinearly oriented sheet may beobtained if the length of the stretcher when in open position (Fig. 1) is ve inches and" the original length of the plastic sheet (Fig. 5) f is one inch. It is to be understood, however, that this example is merely illustrative and not restrictive.

J'As indicated by the lines 2|, 2I, the width of the filmA will be progressively reduced from itsl respective'ends to its central portion. The direcf tion of orientation of its molecules will be curvilinear, as indicated by the broken lines 22. The sheet, which is now extremely flexible, will be bonded-tothe convex surface of a'lens, suchas that shown at 24, a suitable adhesive or bonding material 25 having first been placed on said surface of the lens.

"This may, preferably, be done by grasping the ends of the stretcher and placing the central portion of the surface of the nlm against the convex surface of said lens (Fig. 9) and theny forcing the lm down over said convex surface (Figs. 6 and 10). Thereafter, by an infra red heat lamp 26, or other suitable heating means, the nlm and bonding material are quickly dried. The nlm is then removed from the frame and the portions extending beyond the periphery of the lens are trimmed off. A coating of bonding material 25 is now placed over the'A Aconcave surface of theother lens 2'I and the lensv Having determined the degree of stretch ofl the lm, the plates are set at the proper angle' and the stretcher disposed in the holder between 24 with the lm bonded thereto is pressed firmly down on the concave surface of the lens 21 (Fig. 12) thereby forming the laminated curvilinearly polarized lens shown in Figs. 7 and 8.

As indicated in Fig. 7, the curvilinear orientation obtained when the surface of the film is planary will be changed to a parallel orientation when the lm is laminated to a curvilinear surface. All optical blanks are made in a standard form with spherical surfaces and have a fixed radius of curvature. Therefore, one can readily ascertain the length of the stretcher that will give a film of suitable width a curvilinear orientation of the type herein shown that will be transformed into an orientation in parallelism when the surface of said iilm is changed from a plane to a spherical surface of known radius of curvature. For example, I have ascertained in practice that when a lm of the plastics named above having a Width of four inches is stretched on a frame five inches in length, the orientation of the molecules will `be in parallelism when such film is laminated to the standard optical blank.

Having thus described illustrative embodiments of my invention without, however, limiting the same thereto, what I claim and desire to secure by Letters Patent is:

l. An apparatus for stretching sheets of moistened plastic without the application of heat to orient the molecules thereof, comprising in combination, a frame having two oppositely `disposed attened U-shaped members, each having two parallel side portions connected by a cross bar, each of said side portions having an inner end juxtaposed with the inner end of a side portion of the other U-shaped member means for pivotally connecting the juxtaposed inner ends of said side portions independently of the other pair of juxtaposed inner ends so as to produce an open unobstructed area inwardly of the U-shaped members, and a springr clip pivoted to the cross bars of each of said U-shaped members near one end thereof, each clip being coterminous with its co-operating cross ybar and disposed to snap over the same so as to have area contact with the sheet material.

2. An apparatus as defined in claim 1, wherein the edges of said spring clips are flared outwardly.

3. An apparatus as defined in claim l, Wherein the free end of each clip terminates in a finger piece extending beyond the U-shaped member with which it co-operates.

4. An apparatus for stretching sheets of plastic to orient the molecules thereof comprising in combination a frame having two oppositely disposed U-shaped members each having two spaced side portions connected by a cross bar, each of said side portions having an inner end juxtaposed with the inner end of a respective side portion of the other U-shaped member, means for pivotally connecting the respective juxtaposed inner ends of said side portionsl independently of each other so as to produce an open unobstructed area inwardly of the U-shaped members, and clip means carried by the respective cross bars and extending throughout the major portion of the length of said cross-bars, said clip means being of a channelled cross-sectional shape whereby the cooperating cross bar will intert therewith and assume a tight gripping relations with the sheet material over a relatively wide area of contact.

JOSEPH MAHLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 480,199 MacDonald Aug. 2, 1892 546,492 lVLillert Sept. 17, 1895 2,011,553 Land Aug. 13, 1935 2,041,138 Land May 19, 1936 2,078,254 Land Apr. 27, 1937 2,287,546 Binda June 23, 1942 2,320,375 Moulton June 1, 1943 2,328,827 Martin Sept. 7, 1943 

